Apparatus for cutting worm-gear.



F. w. LANCHBSTER.

APPARATUS POR CUTTING WORM GEAR,

APPLICATION FILED JUNE 29,19%, 1,128,61 3, Patented Feb. 16, 19M,

5 SHEETS* SHIETT F. W. LANCHESTBR. APPARATUS Pon CUTTING WORM (ma,

APPLNWTION FILED JUPE 2D, 191,2,

Patented Feb. 16, 1915 6 SHEETS-.SHEET L) F. W. LANOHESTER.

MWAMATUS POR CUTTING WORM GEAR.

APPLICATION FILED JUNE 29, 1912.

1,128,613, Patented Feb. 16, 1915.

5 SHEETS-SHEET 3.

F. W, LANGHESTMR. APPARATUS FOR CUT'HNG Vf.' RM GEA i.

APPLwAToN FILED JUNE 2 1,128,613. Patented Feb. 16, 1915.

d 5 SHEETS-SHEET 4.

ATTORNEYS F. W. LANCHESTER.

ABPABATUS FOB CUTTING WORM GEAR.

urLIoA'uoN FILED JUNE 29, 1912.

1,128,613. Patented Feb. 16, 1915 5 SHEETS-SHEET 5.

.or initiating the tooth T 'OFFICE Fianna;RICKA LANCHESTER. or EDeBAs'rom BIMINGHAMQENGLAND.

i 'APPARATUS roncUTTrNG WORM-GEAR..

specication of Letters Patent. Patented Feb, 1G, 1 915,

Application filed June 29, 1912. SerialNo. 706.725.

To all 'whom it may concern:`

Be it known that I, Fiinnnlucn WILLIAM LANCHESTER, e. subject of the King of 'Great Britain and Ireland, residing'at 53 Hagley road, Edgbaston, Birmingham, England,

have invented a certain new and useful Improvement in Apparatus for Cutting 'Worm- :.(igeanlof whichl the following is a specifica- 'l'iaving teeth of such form as to stan-d heavy io; and give high efficiency, the. teeth .be brought-to approxiijnatcly their finn'the manufacture of worm gear Ait has been my'practice to cutout the form ofthe' teethby a. machine such as is described in British 'Patent No. 13133 A; D. 1897, 'but the form of tooth that is produced, unv less subsequentlyY modified, is not altogether satisfactory where the highest load capacity (for size) is required.

- The presentinvcntion consists ina method and apparatus'for shaping the teeth in the itting machine at once to the approximate ritn'rwhich will givethebest results.

. `4`JIhe inventionjal'so consists in varying thc 'tlfiickness'o'f the teeth at various pointsv by the movement of a cutteroperated difieren ti'illyto lthe cutter head.

The invention further consistsin a. ma-

lnchine having a rotating cutter head and a "cutting tooth mounted so that it can be moved relatively to such head so as to vary 4thc" Athickness of the teeth cut in the blank from which the worm is to be formed, or in a-to'ol or hob to be used in the production of the gear.

The invention also consists in improved f. voi-m in which the teeth are' thinner in vthe'fue-ckof the worm and also at the ends than they are att-lie mean radial position.

i Referring to Ithe`accompanying drawings, Figures '1 and 2 are Isections at right angles to e h other through the cutter head, showi also the-cani whichoperates the cutter;

title pian cf' the cutter tooth.

Fig'. 5 shows diagrannnatically a modified form of the invention in which the cutter is given a variv able circumferential motion: Fig. 6 shows a ished form without the necessity of any sub! sequent' correcting.

,-niountcd on the sliding V tool slide is operated through the medium of.

.n is an elevation, and Fig. 4 an undervordinarily constructed; Fig..9 is a diagrammatic plan `of' Fig. Fig. 10 shows the face of a worm wheel tooth l ent invention; Fig. 11 is a digrammatic plan .of Fig. 10- Fig. 12 is a. side elevation of 'the complete machine Fig. 13 is an end elevation partly in sectionA of the machine. Figs. 14, 15 and 16 show'themethod 'f development adopted in obtaining the diagrammatic views-shown in Figs.' 9 and 11.

Figs. 17 and 18 are detailed views ofthelever operating the cutter shown in Fig'. 1.

fn worm wheel teeth as usually constructed, the finished surfaceof the tooth approximates to two curved surfaces making a y slight angle with oneanother as shown in Figs. 8

and 9. T he result of this is that when working'in conjunction with a Worm in passingover any given tooth the thread ofthe worm cl'ianges over from one surface vto the-other of' the tooth', and for an instant lthe Whole driving pressure is borne b the angle formed by the junction of theiwo surfaces. This causes overloading of the surface at this point, squeezing out of the oil filma'nd destruction of 'the surface. In a worm Wheel constructed according to the present invention these difficulties are overcome by giving Ato the tooth a form somewhat vlike-that illustrated in Figs. 10 and 11. From Fig. 10 it will be seen that by the `process of manufacembodying the presture an aimost continuous curved'surfa'ce is mounted on a slide b so that it is -capa-ble of movement in a radial direction in the cutter head c c. The slide b carrying thecutter is moved in the radial-direction by means of a cam d bearing on a roller e part f by` which th the lever g. This lever is shown in detail in Figs. 17 and 18. The lever g turnsabout a fulcrunil Z and presses the cutter down' by I means of a knife edge m, the motion being communicatedl toithe lever by the piece f through the knife edge n. Asgshovn, the

levergives a reduction of about 10`to 1. The cutter is held up against the cam d through the lever g by the springs k k. The lever may be adjusted by means of the bearing piece Z: at one end. The form of the cutter is clearly shown in Figs. 3 and 4 and cuts only on the edge o. 1n order to form this cutter the cutter blank is provided with a milled face and the center line 1, 2, of the cutting edge 0 is scribed on the face so milled. The most convenient angle for the cutting edge is about 30 to the longitudinal axis of the tool. The cutter is then shaped to the form illustrated by milling and filing away the blank, taking the scribed line as the working line. ln order to cut the opposite flank of the tooth worm the worm blank is turned end for end, or a cutter of opposite hand is employed.

r[he proportions of the arrangement illustrated in Figs. 1 tol are suitable for cutting a gear of about l to 1 ratio.

ln the modification of the `invention shown at Fig. 5, the cutter a instead of mov ing radially. is given a circumferential motion, being mounted on the ring r which isV actuated in one direction by the cam s operating on the` lever t and in the opposite direction by the spring u.

According to another modification illustrated in Figs. l and 7, the cutter a is given an angulanmotion, being mounted on a slide 3 guided by a dove-tailed groove 4 in the cutter head b. 'l`he angular movement of the. cutter is effected bythe cam 5 acting on the sliding piece 6 which bears on one end ot' the lever 7 whose other end 8 operates the slide 'lhe slidevisv pressed by the spring J in the direction to keep the roller up against the cam. The motion of the tool is thus made eccentric to the cutter head, and the extent to which the top and bottom of the tooth cut are altered in form rendered variable. The required position of the cutter for the top and bottom of the tooth is determined geometrically from the form of tooth required, and the motion of the cutter is then so chosenas to give the required variations.

The. whole machine is shown assembled in Figs. 12 and 13. The cutter head b is mounted so as to rotate in suitable bearings about an axis at right-angles to the axis of the spindle r, on which the Work is mounted. the cutter head and worm being caused to rotate at the desired speed by any suitable known means.

ln order to understand the form of .tooth which is to be made in the worm gear it .should be. pointed out that in the Hindley t' ie ot' uorni U'ear on which the )resent gear is au improvement, cae-h concentric eleinent ot the wheel tooth surface continuously engages with thel corresponding element of the worm, and does not, as in the bitrary series of concentric lamin supposed in the limit to become indefinitely thin so as to avoid any steps in the tooth form. The gear tooth form in the ordinary sense of tooth form is thus emancipated from allV ordinary considerations of rolling contact, y

and the arbitrary form assigned by the 'designer is merely based on the considerations of manufacture and of assembling the parts, that is to say the'tooth is preferably made of an angular section so as to be readily generated and of such a steepness of ,slope as will avoid undercut such as would preventa gear wheel and its Worm being put into mesh or taken apart.

In practice an angle of about 1 in 2 slope or say 300 that is to say a contained worm angle of about 55 to 60 (such as employed in an ordinary Vhitworth or Sellars bolt) is found to give satisfactory results. It will In Figs. 14, 15 and 16 the method of obtaining the developed view Figs. 9 and 11 is shown.

The lamin a, a', a", a", are developed by making equal increments. of absciss, Fig. 15, represent equal increments of the angle a Fig. 14, While in Fig. 16 equal increments of abscissae represent. equal increments of the angle The intersection of a tooth face with the lamin is then plotted giving for the ordinary Worm the result shown in Fig. 9, and for a worm constructed according to thev invention the result shown in Fig. 11.

Having now described my inventionwhat l claim as new and desire to secure by Letters Patent is 2- 1, A machine for cutting'worm Wheel teeth, comprising in combination a rotating cutter head, means for rotating a blank in proximity to said head, a cutter movable in a. radial direction in said cutter head, and fixed means controlling the movements of said cutter relativelyto said head, as and for the purposes described.

2. A machine for cutting worm Wheel teeth, comprising in combination aj rotating llt butter head, means for rotating a blank in proximity to said head, a cutter movable in a radial direction in said cutter head, and

a ixed oam surface controlling the movement of said cutter relatively to seid head, as und for the purposes described.

3. A machine for cutting Worm Wheel teeth, comprising in combination e rotating cutter head, Ineens for rotating a blank in proximity to said head, a. cutter movable in fi radial direction in said cutter head, and

a fixed cuni surface controlling the movement of said cutter relatively to said head, said cuni haring :i recess formed therein and. two' projecting surfaces on the two sides of said recess, as set forth.

In testimony whereof, I afliX my signature in presence of two Witnesses.

FREDERICK WILLIAM LANCHESTEB. li'itnesses JOHN MORGAN, FRAN ois MALPAS. 

